Electrode for electric chemical capacitor, manufacturing method and apparatus thereof

ABSTRACT

A manufacturing method for an electrode for an electrochemical capacitor according to the present invention comprises a first process (steps S 1 -S 3 ) for forming a polarizable electrode layer on a current collector, a second process (step S 4 ) for subjecting the front surface of the polarizable electrode layer formed on the current collector, to an embossment work, and a third process (step S 5 ) for flattening the front surface of the polarizable electrode layer as has undergone the embossment work. In this manner, in the invention, the front surface of the polarizable electrode layer undergoes the embossment work, so that the polarizable electrode layer is effectively compressed, and it is consequently permitted to achieve a high volume capacitance of at least 17 F/cm 3 . Moreover, after the embossment work, the resulting embossment is flattened, so that porous grains contained in the polarizable electrode layer are prevented from falling off, and it is permitted to ensure a high reliability.

This application is a divisional and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. application Ser. No. 11,016,842, filedDec. 21, 2004, and claims the benefit of priority under 35 U.S.C. §119from Japanese Patent Application No. 2003-423969, filed Dec. 22, 2003and Japanese Patent Application No. 2003-432272, filed Dec. 26, 2003.The entire contents of these applications are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to an electrode for an electrochemicalcapacitor and a method and an apparatus for the manufacture thereof, andmore particularly to an electrode for an electrochemical capacitorhaving a high volume capacitance and a method and an apparatus for themanufacture thereof.

BACKGROUND ART

Since electrochemical capacitors including an electric double-layercapacitor can be easily made small in size and light in weight, they areexpected as, for example, backup power sources for the power sources ofportable equipment (small-sized electronic equipment) etc., andauxiliary power sources for an electric automobile and a hybrid vehicle,and various studies have been made for enhancing the performances of theelectrochemical capacitors. Especially in a case where a large capacityis required as in the power source for the electric automobile, it hasbeen desired to develop an electrochemical capacitor in which acapacitance per unit volume of electrodes (hereinbelow, termed “volumecapacitance”) is high.

Each electrode for use in such an electrochemical capacitor has alaminated structure which includes a current collector and a polarizableelectrode layer, and it can be fabricated by coating the front surfaceof the sheet-like current collector with a solution which is to becomethe material of the polarizable electrode layer, and which is subjectedto drying (refer to Patent Document 1). Since, however, the density ofthe polarizable electrode layer to be formed is low merely by coatingthe front surface of the current collector with such a solution and thendrying the solution, a sufficient volume capacitance cannot be attained.In order to attain a higher volume capacitance, therefore, thepolarizable electrode layer needs to be compressed by roll press or thelike after the formation thereof by the coating.

[Patent Document 1] JP-A-2000-106332

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

The inventors' researches, however, have revealed that the compressionof a polarizable electrode layer is insufficient merely by roll pressemploying a roller whose front surface is substantially smooth, so avolume capacitance (at least 17 F/cm³) which is required of anelectrochemical capacitor of high capacitance is difficult ofachievement.

Accordingly, an object of the present invention is to provide amanufacturing method and a manufacturing apparatus for an electrode foran electrochemical capacitor having a higher volume capacitance.

Besides, another object of the invention is to provide a manufacturingmethod and a manufacturing apparatus for an electrode for anelectrochemical capacitor having the volume capacitance of at least 17F/cm³.

Means for Solving the Problem

A manufacturing method for an electrode for an electrochemical capacitoraccording to the present invention is characterized by comprising thefirst step of forming a polarizable electrode layer on a currentcollector; the second step of subjecting a front surface of thepolarizable electrode layer formed on the current collector, to anembossment work; and the third step of flattening the front surface ofthe polarizable electrode layer as has undergone the embossment work.

Here, the expression “subjecting the front surface of the polarizableelectrode layer to the embossment work” signifies that the polarizableelectrode layer is compressed, thereby to form a rugged pattern in thefront surface thereof. The rugged pattern to be formed may be eitherregular or random. Besides, the expression “flattening the front surfaceof the polarizable electrode layer as has undergone the embossment work”signifies that the height of the rugged pattern formed in the frontsurface of the polarizable electrode layer is decreased by compression.Accordingly, the embossment need not always be completely removed, butthe height of the rugged pattern may decrease. In this case, as long asthe height of the rugged pattern is decreased as a whole, a newembossment may well be formed. The “height of the rugged pattern”signifies the perpendicular distance between convex parts and concaveparts.

In this manner, in the invention, the front surface of the polarizableelectrode layer undergoes the embossment work, so that the polarizableelectrode layer is effectively compressed, and it is consequentlypermitted to achieve a high volume capacitance of at least 17 F/cm³.Moreover, after the embossment work, the resulting embossment isflattened, so that porous grains contained in the polarizable electrodelayer are prevented from falling off, and it is permitted to ensure ahigh reliability.

The first step should favorably be performed by coating the currentcollector with a coating liquid which contains porous grains having anelectronic conductivity, a binder capable of binding up the porousgrains, and a liquid capable of dissolving or dispersing the bindertherein. According to this measure, it is permitted to easily form thepolarizable electrode layer on the current collector. In this case, anelectrically conductive assistant should favorably be further containedin the coating liquid. With the electrically conductive assistant, it ispermitted to promote the migration of charges between the currentcollector and the polarizable electrode layer.

The second step should favorably be performed by roll press based on aroller whose front surface is provided with a rugged pattern. Accordingto this measure, it is permitted to reliably subject the front surfaceof the polarizable electrode layer to the embossment work. In this case,the height of the rugged pattern should favorably be set at 20% through70% inclusive, of the thickness of the polarizable electrode layerbefore performing the second step. The reason therefor is that, when therugged pattern is excessively low, the polarizable electrode layer isnot effectively compressed, whereas when the rugged pattern isexcessively high, a damage to the current collector becomes heavy.

The third step should favorably be performed by roll press based on aroller whose front surface is substantially smooth. According to thismeasure, it is permitted to reliably flatten the embossment formed inthe front surface of the polarizable electrode layer.

Besides, the third step may well be performed after the second step hasbeen performed a plurality of times, or the third step may well beperformed a plurality of times. According to this measure, thepolarizable electrode layer is compressed still more, and the porousgrains contained in the polarizable electrode layer are more reliablyprevented from falling off.

A manufacturing apparatus for an electrode for an electrochemicalcapacitor according to the invention is a manufacturing apparatus for anelectrode for an electrochemical capacitor, for manufacturing theelectrode for the electrochemical capacitor by roll-pressing a laminatedproduct in which, at least, a current collector and a polarizableelectrode layer are stacked, characterized by comprising a first rollpress section which subjects a front surface of the polarizableelectrode layer to an embossment work; and a second roll press sectionwhich is disposed downstream of the first roll press section, and whichflattens the front surface of the polarizable electrode layer as hasundergone the embossment work.

With the manufacturing apparatus according to the invention, thepolarizable electrode layer can be effectively compressed, and porousgrains contained in the polarizable electrode layer can be preventedfrom falling off, so that a high reliability can be ensured. Besides,the apparatus is prevented from being polluted due to the porous grainswhich have fallen off.

The first roll press section should preferably include first and secondrollers which roll-press the laminated product, and at least one ofwhich is provided with a rugged pattern in its front surface, and theheight of the rugged pattern should more preferably be 20% through 70%inclusive, of the thickness of the polarizable electrode layer beforeperforming the roll press based on the first roll press section.Further, it is allowed that the rugged pattern is provided in an areawhich has substantially the same width as the width of the polarizableelectrode layer, and that areas which are adjacent to thefirst-mentioned area are substantially flat. With such a roller, thoseparts of the current collector which are not covered with thepolarizable electrode layer are subjected to no embossment work, so thata damage to the current collector can be relieved.

The second roll press section should favorably include third and fourthrollers which roll-press the laminated product, and the front surfacesof which are both substantially smooth.

Further, an electrode for an electrochemical capacitor according to theinvention is characterized by comprising a sheet-like current collector,and a polarizable electrode layer which is provided on the currentcollector with a predetermined bare portion left, the polarizableelectrode layer having undergone an embossment work, at least part ofthe bare portion of the current collector not having undergone anyembossment work.

In this manner, in the invention, the front surface of the polarizableelectrode layer has undergone the embossment work, so that thepolarizable electrode layer is effectively compressed, and it isconsequently permitted to achieve a high volume capacitance of at least17 F/cm³. Moreover, at least part of the bare portion of the currentcollector has not undergone any embossment work, so that a damage to thecurrent collector is relieved, whereby a high reliability can beensured. In this case, it is favorable that substantially the wholesurface of the bare portion of the current collector has not undergoneany embossment work.

Porous grains having an electronic conductivity, and a binder capable ofbinding up the porous grains should preferably be contained in thepolarizable electrode layer, and an electrically conductive assistantshould more preferably be further contained. With the electricallyconductive assistant, it is permitted to promote the migration ofcharges between the current collector and the polarizable electrodelayer.

A manufacturing method for an electrode for an electrochemical capacitoraccording to the invention is characterized by comprising the first stepof coating a current collector with a polarizable electrode layer sothat a bare portion may be left at part of the current collector; andthe second step of subjecting a front surface of the polarizableelectrode layer formed on the current collector, to an embossment work,without subjecting at least part of the bare portion of the currentcollector, to the embossment work.

According to the invention, the electrode for the electrochemicalcapacitor having a high volume capacitance of at least 17 F/cm³ can bemanufactured owing to the effective compression of the polarizableelectrode layer, while the reliability of a manufactured product isheightened by relieving a damage to the current collector. Also in thiscase, it is favorable that substantially the whole surface of the bareportion of the current collector is not undergone any embossment work.

At the first step, the current collector in a band shape as is conveyedin the lengthwise direction thereof should favorably be coated with thepolarizable electrode layer of predetermined width so as to leave thebare portion at, at least, one end part of the current collector in thewidthwise direction thereof. According to this measure, the polarizableelectrode layer is continuously formed on the current collector, so thata high productivity can be attained.

The first step should favorably be performed by coating the currentcollector with a coating liquid which contains porous grains having anelectronic conductivity, a binder capable of binding up the porousgrains, and a liquid capable of dissolving or dispersing the bindertherein. According to this measure, it is permitted to easily form thepolarizable electrode layer on the current collector. In this case, anelectrically conductive assistant should favorably be further containedin the coating liquid. With the electrically conductive assistant, it ispermitted as stated above to promote the migration of charges betweenthe current collector and the polarizable electrode layer.

The second step should favorably be performed by roll press based on aroller which is partially provided with a rugged pattern. Besides, atthe second step, the front surface of the polarizable electrode layerformed on the current collector may well be subjected to an embossmentwork so as to leave part of the front surface.

A manufacturing apparatus for an electrode for an electrochemicalcapacitor according to the invention is a manufacturing apparatus for anelectrode for an electrochemical capacitor, for manufacturing theelectrode for the electrochemical capacitor by roll-pressing a laminatedproduct in which, at least, a current collector and a polarizableelectrode layer are stacked, characterized by comprising a roll presssection which serves to subject a front surface of the polarizableelectrode layer to an embossment work, and which includes a roller thatis partially provided with a rugged pattern.

With the manufacturing apparatus for the electrode for theelectrochemical capacitor according to the invention, the electrode forthe electrochemical capacitor having a high volume capacitance of atleast 17 F/cm³ can be manufactured owing to the effective compression ofthe polarizable electrode layer, while the reliability of a manufacturedproduct is heightened by relieving a damage to the current collector.Also in this case, it is favorable that the rugged pattern is providedin an area which has substantially the same width as the width of thepolarizable electrode layer, and that areas which are adjacent to thefirst-mentioned area are substantially flat.

ADVANTAGES OF THE INVENTION

In this manner, according to the present invention, the front surface ofa polarizable electrode layer has undergone an embossment work, so thatthe polarizable electrode layer is effectively compressed, and it isconsequently permitted to achieve a high volume capacitance of at least17 F/cm³. Moreover, after the embossment work, the resulting embossmentis flattened, so that porous grains contained in the polarizableelectrode layer are prevented from falling off, and it is permitted toensure a high reliability. Thus, it is permitted to fabricate anelectrochemical capacitor of high capacitance and high reliability.

Further, according to the present invention, the front surface of apolarizable electrode layer has undergone an embossment work, so thatthe polarizable electrode layer is effectively compressed, and it isconsequently permitted to achieve a high volume capacitance of at least17 F/cm³. Furthermore, at least part of the bare portion of the currentcollector has not undergone any embossment work, so that a damage to thecurrent collector attributed to the embossment work is relieved, andduring manufacture, winding round a roller for roll press can be relivedto enhance a job efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the structure of an electrode for anelectrochemical capacitor as is fabricated by a manufacturing methodaccording to a preferred embodiment of the present invention, wherein(a) is a schematic sectional view, and (b) is a schematic perspectiveview.

FIG. 2 is a flow chart for explaining the manufacturing method for theelectrode for the electrochemical capacitor according to the preferredembodiment of the invention.

FIG. 3 is a model view for explaining a preparing method for a coatingliquid (step S1).

FIG. 4 is a schematic view showing the structure of a manufacturingapparatus for the electrode for the electrochemical capacitor accordingto a preferred embodiment of the invention.

FIG. 5 is a view showing an example in which a rugged pattern isprovided over substantially the whole area of the front surface 131 a ofa first roller 131.

FIG. 6 is a view showing an example in which a rugged pattern isprovided in only an area 131 a ₁ having substantially the same width asthe width W1 of a polarizable electrode layer 18, in the front surface131 a of the first roller 131.

FIG. 7 is a view exaggeratedly showing the rugged pattern which isprovided in the front surface 131 a of the first roller 131, wherein (a)is a schematic sectional view, and (b) is a schematic plan view.

FIG. 8 is a view exaggeratedly showing that front surface of thepolarizable electrode layer 18 which has been embossed by a first rollpress section 130, wherein (a) is a schematic sectional view, and (b) isa schematic plan view.

FIG. 9 is a view for explaining a process (step S6) for cutting theelectrode 10 for the electrochemical capacitor, out of a laminatedproduct 20, wherein (a) is a schematic plan view of the laminatedproduct 20 which has been cut into a predetermined size, (b) is aschematic plan view of the laminated product 20 out of which theelectrode 10 for the electrochemical capacitor has been cut, and (c) isa schematic plan view of the cut-out electrode 10 for theelectrochemical capacitor.

FIG. 10 is a model view for explaining a method for fabricating theelectrochemical capacitor from the electrodes 10 for the electrochemicalcapacitor.

FIG. 11 is a view showing an example in which a plurality of first rollpress sections 130 are disposed.

FIG. 12 is a view showing an example in which the front surface 141 a ofa third roller 141 included in a second roll press section 140 isprovided with a rugged pattern of small height.

FIG. 13 is a view showing an example in which a rugged pattern isprovided also in the front surface 132 a of a second roller 132 includedin a first roll press section 130.

FIG. 14 is a view showing an example in which the front surface 131-1 aof a roller 131-1 included in an upper stream side roll press section130-1, and the front surface 132-2 a of a roller 132-2 included in alower stream side roll press section 130-2 are respectively providedwith rugged patterns.

FIG. 15 is a flow chart for explaining a manufacturing method for anelectrode for an electrochemical capacitor according to the secondembodiment of the invention.

FIG. 16 is a schematic perspective view exaggeratedly showing a firstroll press section 130 according to the second embodiment (and a secondroll press section 140).

FIG. 17 is a view showing an example in which a rugged pattern isprovided also in the area 141 a ₁ of the front surface 141 a of a thirdroller 141 included in the second roll press section 140 according tothe second embodiment.

FIG. 18 is a view showing an example in which a rugged pattern isprovided also in the area 132 a ₁ of the front surface 132 a of a secondroller 132 included in the first roll press section 130 according to thesecond embodiment.

FIG. 19 is a view showing an example in which a rugged pattern isprovided also in the area 142 a ₁ of the front surface 142 a of a fourthroller 142 included in the second roll press section 140 according tothe second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings. In the ensuingdescription, the construction of an electrode for an electrochemicalcapacitor as is fabricated by a manufacturing method according to eachof the embodiments will be first described, and the manufacturing methodaccording to the embodiment will be thereafter described in detail.

First Embodiment

FIGS. 1( a) and (b) are a schematic sectional view and a schematicperspective view showing the structure of an electrode for anelectrochemical capacitor as is fabricated by a manufacturing methodaccording to the preferred embodiment of the present invention,respectively.

As shown in FIG. 1, the electrode 10 for the electrochemical capacitoraccording to the embodiment is constructed of a current collector 16which has an electronic conductivity, and a polarizable electrode layer18 which has an electronic conductivity and which is formed on thecurrent collector 16.

The material of the current collector 16 is not especially restricted aslong as it is a good conductor of electricity capable of causingsufficient charges to migrate into the polarizable electrode layer 18,and it is possible to employ a current collector material for use in aknown electrode for an electrochemical capacitor, for example, aluminum(Al). The thickness of the current collector 16 is not especiallyrestricted, either, but in order to make the electrochemical capacitorsmaller in size, the current collector 16 should favorably be set at thesmallest possible thickness as long as a satisfactory mechanicalstrength is ensured. Concretely, in the case where aluminum (Al) isemployed as the material of the current collector 16, the thicknessthereof should preferably be set at 20 μm through 50 μm inclusive, andmore preferably at 20 μm through 30 μm inclusive. When the thickness ofthe current collector 16 made of aluminum (Al) is set within the range,it is permitted to achieve reduction in the size of the electrochemicalcapacitor with the satisfactory mechanical strength ensured.

Besides, the current collector 16 includes a bare portion 12 which isnot covered with the polarizable electrode layer 18, and which isemployed as a lead-out electrode.

The polarizable electrode layer 18 is the layer which is formed on thecurrent collector 16, and which contributes to the accumulation andrelease of charges. As its constituent materials, the polarizableelectrode layer 18 contains at least, porous grains which have anelectronic conductivity, and a binder which can bind up the porousgrains. Although not especially restricted, the content of the porousgrains in the polarizable electrode layer 18 should favorably be 84-92mass-% based on the total quantity of the polarizable electrode layer18, and that of the binder should favorably be 6.5-16 mass-% based onthe total quantity of the polarizable electrode layer 18. In particular,the polarizable electrode layer 18 should favorably consist of 84-92mass-% of porous grains, 6.5-16 mass-% of binder, and 0-1.5 mass-% ofelectrically conductive assistant having an electronic conductivity, onthe basis of its total quantity.

The porous grains contained in the polarizable electrode layer 18 arenot especially restricted as long as they have the electronicconductivity and contribute to the accumulation and release of charges.Mentioned as the material of the porous grains is, for example, granularor fibrous active carbon subjected to an activation process. Usable assuch an active carbon is phenolic active carbon, coconut-husk activecarbon, or the like. The mean grain diameter of the porous grains shouldfavorably be 3-20 μm, and the BET specific surface area thereof as iscalculated from a nitrogen adsorption isotherm by a BET isothermicadsorption formula should preferably be at least 1500 m²/g, morepreferably 2000-2500 m²/g. With such porous grains, it is permitted toattain a high volume capacitance.

Besides, the binder contained in the polarizable electrode layer 18 isnot especially restricted as long as it is capable of binding up theporous grains. Usable as the binder is any of, for example,polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),polyethylene (PE), polypropylene (PP), and fluorine rubber. Among them,the fluorine rubber is especially favorably used. The reason therefor isthat, when the fluorine rubber is used, the porous grains can besufficiently bound up even with a small content, whereby the coatingfilm strength of the polarizable electrode layer 18 is enhanced, and thesize of a double-layer interface can be enlarged to enhance the volumecapacitance.

Mentioned as the fluorine rubber are, for example, vinylidenefluoride-hexafluoropropylene type fluorine rubber (VDF-HFP type fluorinerubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylenetype fluorine rubber (VDF-HFP-TFE type fluorine rubber), vinylidenefluoride-pentafluoropropylene type fluorine rubber (VDF-PFP typefluorine rubber), vinylidenefluoride-pentafluoropropylene-tetrafluoroethylene type fluorine rubber(VDF-PFP-TFE type fluorine rubber), vinylidenefluoride-perfluoromethylvinyl ether-tetrafluoroethylene type fluorinerubber (VDF-PFMVE-TFE type fluorine rubber, and vinylidenefluoride-chlorotrifluoroethylene type fluorine rubber (VDF-CTFE typefluorine rubber). Herein, the fluorine rubbers in each of which at leasttwo members selected from the group consisting of the substances VDF,HFP and TFE are copolymerized are preferable, and the VDF-HFP-TFE typefluorine rubber in which the three substances of the group arecopolymerized is especially preferable because it has the tendency ofmore enhancing an adhering property and tolerances to chemicals.

Further, the electrically conductive assistant which is contained in thepolarizable electrode layer 18 as may be needed is not especiallyrestricted as long as it has the electronic conductivity capable ofsufficiently carrying out the migration of charges between the currentcollector 16 and the polarizable electrode layer 18. Carbon black, forexample, is mentioned as the electrically conductive assistant.

Acetylene black, ketffen black, and furnace black, for example, arementioned as the carbon black, and the acetylene black is favorablyemployed in the invention. The mean grain diameter of the carbon blackshould preferably be 25-50 nm, and the BET specific surface area thereofshould preferably be at least 50 m²/g, more preferably 50-140 m²/g.

Besides, from the viewpoint of making the electrode 10 for theelectrochemical capacitor small in size and light in weight, thethickness of the polarizable electrode layer 18 should preferably be50-200 μm, more preferably 80-150 μm. By the way, in a case where thethickness of the polarizable electrode layer 18 is not uniform (in acase, for example, where an embossment remains on the surface thereof),the above thickness shall signify the maximum thickness. Theelectrochemical capacitor can be made small in size and light in weightby setting the thickness of the polarizable electrode layer 18 withinthe above range.

The thickness (maximum thickness) of the whole electrode 10 for theelectrochemical capacitor as is constructed by stacking the currentcollector 16 and the polarizable electrode layer 18 should preferably be70-250 μm, and it should more preferably be 100-180 μm. Owing to such athickness, the electrochemical capacitor can be made small in size andlight in weight.

The above is the construction of the electrode 100 for theelectrochemical capacitor as is fabricated by the manufacturing methodaccording to the preferred embodiment of the invention. Next, themanufacturing method according to the preferred embodiment of theinvention will be described in detail.

FIG. 2 is a flow chart for explaining the manufacturing method for theelectrode for the electrochemical capacitor according to the preferredembodiment of the invention. Now, the manufacturing method for theelectrode for the electrochemical capacitor according to this embodimentwill be described with reference to the flow chart.

First of all, a coating liquid to become the material of the polarizableelectrode layer 18 is prepared (step S1). The preparation of the coatingliquid can be performed in the ensuing way. First, as shown in FIG. 3,the porous grains P1 stated above, the binder P2 stated above, a liquidS1 to be stated below, and if necessary, the electrically conductiveassistant P3 stated above are thrown into a mixing device C1 includingan agitation unit SB1, and they are agitated therein. Thus, the coatingliquid L1 can be prepared. The preparation of the coating liquid shouldfavorably include a kneading operation and/or a dilution mixingoperation. Here, the “kneading” signifies to blend the constituentmaterials by agitating them in a state where the liquid has acomparatively high viscosity, while the “dilution mixing” signifies tomix the constituent materials together in a state where a solvent or thelike is further added into the kneaded liquid so as to establish acomparatively low viscosity. The time periods of the operations andtemperatures during the operations are not especially restricted, butfrom the viewpoint of establishing a uniform dispersion state, it isfavorable to set the kneading time period on the order of 30 minutes-2hours and the temperature during the kneading on the order of 40-80° C.,and it is favorable to set the dilution-mixing time period on the orderof 1-5 hours and the temperature during the dilution mixing on the orderof 20-50° C.

The liquid S1 shown in FIG. 3 is not especially restricted as long as itis capable of dissolving or dispersing the binder P2 therein. By way ofexample, a ketonic solvent such as methyl-ethyl-ketone (MEK) ormethyl-isobutyl-ketone (MIBK) can be employed as the liquid S1. Besides,the compounding proportion of the liquid S1 in the coating liquid L1should favorably be set at 200-400 mass-parts based on 100 mass-parts ofthe whole solid matter in the coating liquid L1. The content of theporous grains P1 in the coating liquid L1 should favorably be set sothat the content of the porous grains P1 after the formation of thepolarizable electrode layer 18 may fall within the range specifiedbefore.

After the coating liquid L1 has been prepared in this way, the surfaceof the current collector 16 is subsequently coated with the coatingliquid L1, thereby to form a coating film (step S2), and the liquid S1contained in the coating film is removed by drying (step S3). Thus, astate is established where the polarizable electrode layer 18 notcompressed yet has been formed on the current collector 16. Any ofvarious known coating methods can be used without any specialrestriction, as a method for coating the surface of the currentcollector 16 with the coating liquid L1. It is possible to adopt amethod, for example, extrusion lamination, doctor blade coating, gravurecoating, reverse coating, applicator coating, or screen printing.Besides, the drying of the coating film can be performed by heating fora predetermined time period. Concretely, the drying should favorably beperformed under conditions of 70-130° C. and 0.1-10 minutes.

After the uncompressed polarizable electrode layer 18 has been formed onthe current collector 16 in this way, the front surface of thepolarizable electrode layer 18 is subsequently embossed (step S4), andthe embossed front surface of the polarizable electrode layer 18 isfurther flattened (step S5). Here, the embossment work of the frontsurface of the polarizable electrode layer 18 is done for effectivelycompressing the polarizable electrode layer 18, thereby to heighten avolume capacitance. On the other hand, the flattening of the embossedfront surface of the polarizable electrode layer 18 is done forpreventing the porous grains P1 from falling off from the embossed frontsurface of the polarizable electrode layer 18. More specifically, whenthe front surface is strongly embossed (in a case, for example, wherethe height of a rugged pattern to be stated later is large), the porousgrains P1 are liable to fall off, and hence, it is apprehended todegrade the reliability of a product or to pollute a manufacturingapparatus.

A method for embossing the front surface of the polarizable electrodelayer 18 can be incarnated in such a way, for example, that a roller orthe like transfer member whose front surface is provided with the ruggedpattern is pressed against the front surface of the polarizableelectrode layer 18. In this case, the height of the rugged patternprovided in the front surface of the transfer member should preferablybe set at 20%-70% inclusive, of the thickness of the polarizableelectrode layer 18 before the embossment work, and it should morepreferably be set at 30%-60% inclusive. The reason therefor is that,when the height of the rugged pattern is excessively small, thepolarizable electrode layer 18 is not effectively compressed, whereaswhen the height of the rugged pattern is excessively large, a damage tobe done to the current collector 16 becomes heavy. Incidentally, the“height of the rugged pattern” signifies the perpendicular distancebetween a convex part and a concave part.

Besides, a method for flattening the embossed front surface of thepolarizable electrode layer 18 can be incarnated in such a way, forexample, that a roller or the like flattening member whose surface issubstantially smooth is pressed against the front surface of thepolarizable electrode layer 18.

Owing to the above operations, the polarizable electrode layer 18 whichhas been effectively compressed and which prevents the porous grainsfrom falling off is formed on the current collector 16. Accordingly,when the resulting structure is cut out into a size and a shape whichare necessary (step S6), the electrode 10 for the electrochemicalcapacitor is finished up.

FIG. 4 is a schematic view showing the structure of an apparatus whichis capable of performing the above steps S2-S5 (the manufacturingapparatus for the electrode for the electrochemical capacitor).

The manufacturing apparatus 100 for the electrode for theelectrochemical capacitor as shown in FIG. 4 includes a feed roll 101round which a sheet-like current collector 16 is wound, a take-up roll102 round which a laminated product 20 consisting of the currentcollector 16 and a polarizable electrode layer 18 is to be wound byrotating at a predetermined velocity, and a coating section 110, adrying section 120, a first roll press section 130 and a second rollpress section 140 which are disposed between the feed roll 101 and thetake-up roll 102 in the order mentioned. In this manner, themanufacturing apparatus 100 for the electrode for the electrochemicalcapacitor has the construction in which the coating section 110, dryingsection 120, first roll press section 130 and second roll press section140 are successively arranged from the upper stream (feed roll 101) tothe lower stream (take-up roll 102).

The coating section 110 is a portion for performing the process (stepS2) for coating the surface of the current collector 16 with a coatingliquid L1. The coating section 110 includes a vessel 111 which reservesthe coating liquid L1 therein, a coating-liquid feed roll (gravure roll)112 which feeds the current collector 16 with the coating liquid L1 inthe vessel 111, and a backup roll 113 which rotates in interlocking withthe coating-liquid feed roll 112. As shown in FIG. 4, the currentcollector 16 fed from the feed roll 101 is conveyed in a state where itis held between the coating-liquid feed roll 112 and the backup roll 113which are rotating, whereby a coating film L2 serving as the material ofthe polarizable electrode layer 18 is formed on one surface of thecurrent collector 16. The current collector 16 formed with the coatingfilm L2 is moved toward the drying section 120 by a guide roll 103.

The drying section 120 is a portion for performing the process (step S3)for removing a liquid S1 which is contained in the coating film L2. Inthe manufacturing apparatus 100 for the electrode for theelectrochemical capacitor as shown in FIG. 4, the drying section 120 isconstituted by two dryers 121 and 122 which are arranged so as to holdthe current collector 16 therebetween, and the liquid S1 contained inthe coating film L2 is removed by heating based on the dryers 121 and122, until the coating film L2 becomes the polarizable electrode layer18. Thus, a state is established where the polarizable electrode layer18 has been formed on the surface of the current collector 16. However,the density of the polarizable electrode layer 18 is low in this state,and a high volume capacitance cannot be attained in the state leftintact.

The first roll press section 130 is a portion for performing the process(step S4) for embossing the front surface of the polarizable electrodelayer 18. In the manufacturing apparatus 100 for the electrode for theelectrochemical capacitor as shown in FIG. 4, the first roll presssection 130 includes a first roller 131 arranged on the side of thepolarizable electrode layer 18, and a second roller 132 arranged on theside of the current collector 16, and the laminated product 20 isroll-pressed by the rollers 131 and 132, thereby to compress thepolarizable electrode layer 18 included in the laminated product 20.Here, the front surface 131 a of the first roller 131 is provided with arugged pattern, whereby the rugged pattern is transferred onto the frontsurface of the polarizable electrode layer 18 having passed through thefirst roll press section 130. That is, the front surface of thepolarizable electrode layer 18 is embossed. On the other hand, the frontsurface 132 a of the second roller 132 is substantially smooth.

In so far as the first roller 131 included in the first roll presssection 130 is capable of embossing substantially the whole frontsurface of the polarizable electrode layer 18, it may well be providedwith the rugged pattern over substantially the whole area of the frontsurface 131 a as shown in FIG. 5. Alternatively, as shown in FIG. 6, thefirst roller 131 may well be provided with the rugged pattern in only anarea 131 a ₁ which has substantially the same width as the width W1 ofthe polarizable electrode layer 18, the other areas 131 a ₂ beingsubstantially smooth. With the type of the first roller 131 as shown inFIG. 5, it is permitted to reliably emboss the whole front surface ofthe polarizable electrode layer 18 even in a case where the laminatedproduct 20 has deviated relative to the first roller 131 in the axialdirection thereof. On the other hand, with the type of the first roller131 as shown in FIG. 6, those parts of the current collector 16 whichare not covered with the polarizable electrode layer 18 are notembossed, and it is therefore permitted to relieve a damage which is tobe done to the current collector 16.

FIG. 7 is a view exaggeratedly showing the rugged pattern which isprovided in the front surface 131 a of the first roller 131, wherein (a)is a schematic sectional view, and (b) is a schematic plan view.

As shown in FIGS. 7( a) and (b), the front surface 131 a of the firstroller 131 is formed with concave parts 90 a and convex parts 90 b, andthe plurality of concave parts 90 a each having a conical shape areprovided regularly at equal intervals. Besides, the convex parts 90 bare located among the concave parts 90 a. As already described, theperpendicular distance N₃ between the concave part 90 a and the convexpart 90 b, that is, the height of the rugged pattern should preferablybe set at 20% through 70% inclusive, of the thickness of the polarizableelectrode layer 18 before the embossment work, more preferably at 30%through 60% inclusive. Besides, in this example, the convex part 90 bhas a flat part 90 c, the width N₅ of which should favorably be set at5-15 μm. In addition, the inclination α of the concave part 90 a shouldpreferably be set at 35°-75°, more preferably at 45°-65°.

FIG. 8 is a view exaggeratedly showing that front surface of thepolarizable electrode layer 18 which has been embossed by the first rollpress section 130, wherein (a) is a schematic sectional view, and (b) isa schematic plan view.

As shown in FIGS. 8( a) and (b), the rugged pattern provided in thefront surface 131 a of the first roller 131 is transferred onto thefront surface of the polarizable electrode layer 18 having passedthrough the first roll press section 130. More specifically, concaveparts 91 a are formed in areas corresponding to the convex parts 90 b ofthe first roller 131, and convex parts 91 b are formed in areascorresponding to the concave parts 90 a of the first roller 131.Besides, areas corresponding to the flat parts 90 c of the first roller131 become flat parts 91 c. Thus, the polarizable electrode layer 18 iscompressed most strongly especially at the flat parts 91 c, whereby thedensity of the polarizable electrode layer 18 is effectively heightened.

In this state, however, the density of the polarizable electrode layer18 especially at the distal end parts of the convex parts 91 b is notsufficient, and the porous grains P1 are apprehended to fall off fromthe convex parts 91 b, on account of the shape of the distal end parts.Such problems are solved by the roll press based on the second rollpress section 140 which is located downstream of the first roll presssection 130.

More specifically, the second roll press section 140 is a portion forperforming the process (step S5) for flattening the embossed frontsurface of the polarizable electrode layer 18. In the manufacturingapparatus 100 for the electrode for the electrochemical capacitor asshown in FIG. 4, the second roll press section 140 is constituted by athird roller 141 arranged on the side of the polarizable electrode layer18, and a fourth roller 142 arranged on the side of the currentcollector 16. Both the front surfaces 141 a and 142 a of the third andfourth rollers 141 and 142 are substantially smooth, and the laminatedproduct 20 is roll-pressed by such rollers 141 and 142, whereby theembossment formed on the front surface of the polarizable electrodelayer 18 is flattened. That is, the convex parts 91 b of the polarizableelectrode layer 18 are collapsed, whereby the density is furtherheightened, and the porous grains P1 are prevented from falling off fromthe convex parts 91 b.

The laminated product 20 having completed such roll press is guided by aguide roll 104 so as to be wound round the take-up roll 102.

In this manner, when the manufacturing apparatus 100 for the electrodefor the electrochemical capacitor as shown in FIG. 4 is employed, it ispermitted to continuously perform the steps S2-S5 stated above.

Besides, the laminated product 20 wound round the take-up roll 102 iscut into a predetermined size as shown in FIG. 9( a), and the laminatedproduct 20 is punched in accordance with the scale of theelectrochemical capacitor to-be-fabricated as shown in FIG. 9( b). Then,the electrode 10 for the electrochemical capacitor is finished up asshown in FIG. 9( c). On this occasion, that part of the currentcollector 16 which is not covered with the polarizable electrode layer18 is simultaneously derived as shown in FIG. 9( c), it can be utilizedas the lead-out electrode 12.

In the electrode 10 for the electrochemical capacitor as has beenmanufactured in the above way, the front surface of the polarizableelectrode layer 18 has been embossed (step S4) and has thereafter beenflattened (step S5), so that a high volume capacitance of at least 17F/cm³ can be achieved. Moreover, it is permitted to prevent the porousgrains P1 from falling off, and to ensure a high reliability. Also, thepollution of the apparatus attributed to the porous grains P1 havingfallen off is prevented.

Besides, as shown in FIG. 10, at least two fabricated electrodes 10 forthe electrochemical capacitor are prepared, and a separator 40 is heldbetween the two electrodes 10 for the electrochemical capacitor with thepolarizable electrode layers 18 confronting each other. Thereafter, theresulting structure is accommodated in a case not shown, and the case isfilled up with an electrolyte solution. Then, the electrochemicalcapacitor is finished up.

The separator 40 should favorably be formed from an insulating poroussubstance. Usable as the separator 40 is, for example, a laminatedproduct which consists of films of polyethylene, polypropylene orpolyolefin, an extended film which is made from a mixture consisting ofthe above resins, or a fibrous or unwoven fabric material which is madefrom at least one constituent material selected from the groupconsisting of cellulose, polyester and polypropylene.

Besides, usable as the electrolyte solution is an electrolyte solution(an electrolytic aqueous solution, or an electrolyte solution using anorganic solvent) which is employed in a known electrochemical capacitorsuch as electric double-layer capacitor. However, in a case where theelectrochemical capacitor is the electric double-layer capacitor, theelectrolytic aqueous solution exhibits a low decomposition voltageelectrochemically, and hence, the useful-life voltage of the capacitoris limited to be low, so that the electrolyte solution using the organicsolvent (non-aqueous electrolyte solution) is favorable. Although theconcrete sort of the electrolyte solution is not especially restricted,the electrolyte solution should favorably be selected in considerationof the solubility and the dissociation degree of a solute and theviscosity of a liquid, and an electrolyte solution of high electricconductivity and high potential window (high decomposition initiationvoltage) is especially desirable. Used as a typical example istetraethyl ammonium tetrafluoroborate or the like class-4 ammonium saltwhich is dissolved in the organic solvent such as propylene carbonate,diethylene carbonate or acetonitrile. By the way, in this case, a mixingwater content needs to be severely managed.

Thus far, the preferred embodiment of the invention has been describedin detail, but the invention is not restricted to the embodiment.

By way of example, although the embossment work for the front surface ofthe polarizable electrode layer 18 is performed only once in theembodiment, a plurality of times of embossment works may well beperformed by disposing a plurality of first roll press sections 130 asshown in FIG. 11. In the example shown in FIG. 11, an upper stream sideroll press section 130-1 and a lower stream side roll press section130-2 are disposed, and the front surface 131-1 a of a roller 131-1included in the upper stream side roll press section 130-1, and thefront surface 131-2 a of a roller 131-2 included in the lower streamside roll press section 130-2 are respectively provided with ruggedpatterns. In this case, the rugged pattern provided in the front surface131-1 a of the roller 131-1, and the rugged pattern provided in thefront surface 131-2 a of the roller 131-2 need not be in an identicalshape. By way of example, when the height of the rugged pattern is setlarger in the roller 131-1 located on the upper stream side, than in theroller 131-2 located on the lower stream side, the polarizable electrodelayer 18 is formed with a deep embossment by the upper stream side rollpress section 130-1, and further, the embossment is flattened and a newshallow embossment is formed by the lower stream side roll press section130-2. Besides, the shallow embossment formed by the lower stream sideroll press section 130-2 is further flattened by a second roll presssection 140.

Conversely, the height of the rugged pattern may well be set larger inthe roller 131-2 located on the lower stream side, than in the roller131-1 located on the upper stream side. In this case, the polarizableelectrode layer 18 is formed with a comparatively shallow embossment bythe upper stream side roll press section 130-1, and further, it isformed with a deep embossment by the lower stream side roll presssection 130-2. Also in this case, the deep embossment formed by thelower stream side roll press section 130-2 is flattened by the secondroll press section 140.

Alternatively, embossments of different shapes may well be formed insuch a way that the heights of the rugged patterns are substantiallyequalized in the roller 131-1 located on the upper stream side and theroller 131-2 located on the lower stream side, while the pitches N₄ ofthe convex parts 90 b or the inclinations α thereof (refer to FIG. 7)are made different from each other.

Incidentally, although not shown, a plurality of second roll presssections 140 may well be disposed, thereby to perform a plurality oftimes of flattening operations for the embossments.

Further, as shown in FIG. 12, the front surface 141 a of a third roller141 which is included in a second roll press section 140 may well beprovided with a rugged pattern of small height. According to thismeasure, a new shallow embossment is formed while a deep embossmentformed by a first roll press section 130 is being flattened. In thiscase, however, for the purpose of satisfactorily preventing the porousgrains P1 from falling off from the front surface of the polarizableelectrode layer 18, the height of the rugged pattern which is providedin the front surface 141 a of the third roller 141 should preferably beset at or below 15% of the thickness of the polarizable electrode layer18 after the roll press by the first roll press section 130, morepreferably at or below 10%.

Further, in the embodiment, only one surface of the current collector 16is formed with the polarizable electrode layer 18, but both the surfacesof the current collector 16 can also be formed with polarizableelectrode layers 18. In this case, as shown in FIG. 13, also the frontsurface 132 a of a second roller 132 included in a first roll presssection 130 may be provided with a rugged pattern. According to thismeasure, the polarizable electrode layers 18 formed on both the surfacesof the current collector 16 can be simultaneously embossed.

However, when both the first roller 131 and the second roller 132 areprovided with rugged patterns, the polarizable electrode layers 18 mightfail to be sufficiently compressed in some ways of the superposition ofthe rugged patterns, or contrariwise, a damage to the current collector16 might become heavy due to excessive compression. In order to avoidthis drawback, it is favorable that, as shown in FIG. 14, a first rollpress section 130 is divided into an upper stream side roll presssection 130-1 and a lower stream side roll press section 130-2,whereupon the front surface 131-1 a of a roller 131-1 included in theupper stream side roll press section 130-1, and the front surface 132-2a of a roller 132-2 included in the lower stream side roll press section130-2 are respectively provided with rugged patterns. According to thismeasure, the front surfaces 132-1 a and 131-2 a of the other rollers132-1 and 131-2 are substantially smooth, respectively, so that theabove problem does not occur.

Besides, the manufacturing apparatus for the electrode for theelectrochemical capacitor according to the invention need not alwayshave the construction in which, as in the apparatus shown in FIG. 4, thecoating section 110, drying section 120, first roll press section 130and second roll press section 140 are arranged continuously andunitarily, but it may well be the aggregate of two or more apparatusesas long as the above order is ensured. By way of example, the sheet-likecurrent collector 16 having passed through the drying section 120 maywell be taken up once and be roll-pressed by another apparatus whichincludes the first roll press section 130 and the second roll presssection 140. Further, the first roll press section 130 and the secondroll press section 140 may well be apparatuses which are separate fromeach other.

Incidentally, the electrode for the electrochemical capacitor asmanufactured by the invention can be employed as an electrode for anelectric double-layer capacitor, and it is also utilizable as anelectrode for any of various electrochemical capacitors such as apseudo-capacitance capacitor, a pseudo-capacitor and a Redox capacitor.

Second Embodiment

In an electrode 10 for an electrochemical capacitor according to thisembodiment, a polarizable electrode layer 18 is embossed, wherebyincrease in the volume capacitance of the polarizable electrode layer 18is attained. Although the details will be described later, thecompression of the polarizable electrode layer 18 is insufficient, andthe attainment of a volume capacitance of at least 17 F/cm³ isdifficult, merely by forming the polarizable electrode layer 18 andthereafter roll-pressing it with a roller whose front surface issubstantially smooth. However, when the polarizable electrode layer 18is roll-pressed using a roller whose front surface is provided with arugged pattern, this polarizable electrode layer 18 is effectivelycompressed, whereby the volume capacitance of at least 17 F/cm³ becomesattainable.

Meanwhile, in the electrode 10 for the electrochemical capacitoraccording to this embodiment, the bare portion 12 of a current collector16 undergoes no embossment work over substantially the whole areathereof. The reasons therefor are that the current collector 16 itselfneed not be embossed, and that unfavorably the current collector 16might be damaged when strongly embossed. In consideration of thesepoints, only the polarizable electrode layer 18 is embossed in theelectrode 10 for the electrochemical capacitor according to thisembodiment. A method for embossing only the polarizable electrode layer18 will be described later.

FIG. 15 is a flow chart for explaining the manufacturing method for theelectrode for the electrochemical capacitor according to the preferredembodiment of the invention. Now, the manufacturing method for theelectrode for the electrochemical capacitor according to this embodimentwill be described with reference to the flow chart.

First of all, a coating liquid L1 to become the material of thepolarizable electrode layer 18 is prepared (step S1), the surface of thecurrent collector 16 is subsequently coated with the coating liquid L1,thereby to form a coating film (step S2), and a liquid S1 contained inthe coating film is removed by drying (step S3). Thus, a state isestablished where the polarizable electrode layer 18 not compressed yethas been formed on the current collector 16. On this occasion, thepolarizable electrode layer 18 is formed having a predetermined width,so that the bare portions 12 of the current collector 16 may be leftbehind at both the end parts of the current collector 16 in thewidthwise direction thereof. Since these steps are the same as in thefirst embodiment, they shall be omitted from detailed description.

After the uncompressed polarizable electrode layer 18 has been formed onthe current collector 16 in this way, the front surface of thepolarizable electrode layer 18 is embossed (step S4) by subjecting thebare portions 12 of the current collector 16 to substantially noembossment work. As stated above, the embossment work of the frontsurface of the polarizable electrode layer 18 is done for effectivelycompressing the polarizable electrode layer 18, thereby to heighten avolume capacitance. In this case, after the front surface of thepolarizable electrode layer 18 has been embossed, it should favorably befurther flattened. When such flattening is done, it is permitted toeffectively prevent porous grains P1 from falling off from the embossedfront surface of the polarizable electrode layer 18. More specifically,when the front surface is strongly embossed (in a case, for example,where the height of a rugged pattern to be stated later is large), theporous grains P1 are liable to fall off, and hence, it is apprehended todegrade the reliability of a product or to pollute a manufacturingapparatus. In this embodiment, however, it is not indispensable toperform the flattening of the embossment.

A method for embossing the front surface of the polarizable electrodelayer 18 can be incarnated in such a way, for example, that a roller orthe like transfer member whose front surface is provided with the ruggedpattern is pressed against the front surface of the polarizableelectrode layer 18. In this case, the height of the rugged patternprovided in the front surface of the transfer member should preferablybe set at 20%-70% inclusive, of the thickness of the polarizableelectrode layer 18 before the embossment work, and it should morepreferably be set at 30%-60% inclusive. The reason therefor is that,when the height of the rugged pattern is excessively small, thepolarizable electrode layer 18 is not effectively compressed, whereaswhen the height of the rugged pattern is excessively large, a damage tobe done to the current collector 16 becomes heavy.

According to the second embodiment, in the manufacturing apparatus 100for the electrode for the electrochemical capacitor as shown in FIG. 4,the front surface 131 a of the first roller 131 is partially providedwith the rugged pattern as stated below, whereby the rugged pattern istransferred onto the front surface of the polarizable electrode layer 18having passed through the first roll press section 130. That is, thefront surface of the polarizable electrode layer 18 is embossed. On theother hand, the front surface 132 a of the second roller 132 issubstantially smooth.

FIG. 16 is a schematic perspective view exaggeratedly showing the firstroll press section 130 (and second roll press section 140).

As shown in FIG. 16, the first roller 131 included in the first rollpress section 130 is provided with the rugged pattern in only an area131 a ₁ which has substantially the same width as the width W1 of thepolarizable electrode layer 18, the other areas 131 a ₂ beingsubstantially smooth. Thus, only the front surface of the polarizableelectrode layer 18 can be embossed by subjecting the bare portions 12 ofthe current collector 16 to substantially no embossment work. It isconsequently permitted to relieve a damage which is to be done to thecurrent collector 16, with the polarizable electrode layer 18effectively compressed. Moreover, since the areas 131 a ₂ correspondingto the bare portions 12 of the current collector 16 are substantiallysmooth, the possibility at which a laminated product 20 having passedthrough the first roll press section 130 will be wound round the firstroller 131 becomes low to enhance a job efficiency.

In the same manner as in the first embodiment, as shown in FIGS. 7( a)and (b), the concave parts 90 a and the convex parts 90 b are formed inthe area 131 a ₁ of the front surface 131 a of the first roller 131, andthe plurality of concave parts 90 a each having a conical shape areprovided regularly at equal intervals. Detailed description shall beomitted here.

Also in the same manner as in the first embodiment, as shown in FIGS. 8(a) and (b), the rugged pattern provided in the area 131 a ₁ of the frontsurface 131 a of the first roller 131 is transferred onto the frontsurface of the polarizable electrode layer 18 having passed through thefirst roll press section 130. Since the areas 131 a ₂ of the frontsurface 131 a of the first roller 131 are substantially smooth as statedabove, such an embossment is not formed in each of the bare portions 12of the current collector 16. However, those regions of the bare portions12 of the current collector 16 which are near to the polarizableelectrode layer 18 may well be somewhat embossed in relation to amachining precision. Accordingly, the expression “substantially thewhole areas of the bare portions 12 of the current collector 16 are notembossed” shall cover the case where the slight regions of the bareportions extending along the polarizable electrode layer 18 are embossedin relation to the machining precision.

In this state, however, the density of the polarizable electrode layer18 especially at the distal end parts of the convex parts 91 b might notbe sufficient. In this case, the porous grains P1 are apprehended tofall off from the convex parts 91 b, on account of the shape of thedistal end parts. Such problems are solved by roll press based on thesecond, roll press section 140 which is located downstream of the firstroll press section 130.

More specifically, the second roll press section 140 is a portion forflattening the embossed front surface of the polarizable electrode layer18. In the manufacturing apparatus 100 for the electrode for theelectrochemical capacitor as shown in FIG. 4, the second roll presssection 140 is constituted by a third roller 141 arranged on the side ofthe polarizable electrode layer 18, and a fourth roller 142 arranged onthe side of the current collector 16. Both the front surfaces 141 a and142 a of the third and fourth rollers 141 and 142 are substantiallysmooth, and the laminated product 20 is roll-pressed by such rollers 141and 142, whereby the embossment formed on the front surface of thepolarizable electrode layer 18 is flattened. That is, the convex parts91 b of the polarizable electrode layer 18 are collapsed, whereby thedensity is further heightened, and the porous grains P1 are preventedfrom falling off from the convex parts 91 b. It is not indispensable,however, that the manufacturing apparatus according to this embodimentincludes the second roll press section for flattening the embossment.

Incidentally, the pressure of the roll press for the embossment work andthe flattening should favorably be set at 4900 N/cm (500 kgf/cm)−24500N/cm (2500 kgf/cm).

The laminated product 20 having completed such roll press is guided by aguide roll 104 so as to be wound round a take-up roll 102.

In this manner, when the manufacturing apparatus 100 for the electrodefor the electrochemical capacitor as shown in FIG. 4 is employed, it ispermitted to continuously perform the steps S2-S5 stated above.

Besides, the laminated product 20 wound round the take-up roll 102 iscut into a predetermined size as shown in FIG. 9( a), and the laminatedproduct 20 is punched in accordance with the scale of theelectrochemical capacitor to-be-fabricated as shown in FIG. 9( b). Then,the electrode 10 for the electrochemical capacitor is finished up asshown in FIG. 9( c). On this occasion, that part of the currentcollector 16 which is not covered with the polarizable electrode layer18, namely, part of the bare portion 12 is simultaneously derived asshown in FIG. 9( c), and it can be utilized as a lead-out electrode.

In the electrode 10 for the electrochemical capacitor as has beenmanufactured in the above way, the front surface of the polarizableelectrode layer 18 has been embossed (step S4), so that a high volumecapacitance of at least 17 F/cm³ can be achieved. Moreover, since thebare portions 12 of the current collector 16 are subjected tosubstantially no embossment work, it is permitted to relieve a damage tothe current collector 16 and the winding of the laminated product roundthe first roller 131. Besides, when the embossment formed on the frontsurface of the polarizable electrode layer 18 is flattened using thesecond roll press section 140, it is permitted to prevent the porousgrains P1 from falling off, and to ensure a high reliability. Also, thepollution of the apparatus attributed to the porous grains P1 havingfallen off is prevented.

Besides, as shown in FIG. 10, at least two fabricated electrodes 10 forthe electrochemical capacitor are prepared, and a separator 40 is heldbetween the two electrodes 10 for the electrochemical capacitor with thepolarizable electrode layers 18 confronting each other. Thereafter, theresulting structure is accommodated in a case not shown, and the case isfilled up with an electrolyte solution. Then, the electrochemicalcapacitor is finished up.

Thus far, the preferred embodiment of the invention has been describedin detail, but the invention is not restricted to the embodiment.

By way of example, although the embossment work for the front surface ofthe polarizable electrode layer 18 is performed only once in theembodiment, a plurality of times of embossment works for the frontsurface of the polarizable electrode layer 18 may well be performed insuch a way that, as shown in FIG. 17, the third roller 141 included inthe second roll press section 140 is also provided with a rugged patternin an area 141 a ₁ having substantially the same width as the width W1of the polarizable electrode layer 18, the other areas 141 a ₂ beingmade substantially smooth. In this case, the rugged pattern provided inthe area 131 a ₁ of the front surface 131 of the first roller 131, andthe rugged pattern provided in the area 141 a ₁ of the front surface 141of the third roller 141 need not be in an identical shape. By way ofexample, when the height of the rugged pattern is set larger in thefirst roller 131 located on the upper stream side, than in the thirdroller 141 located on the lower stream side, the polarizable electrodelayer 18 is formed with a deep embossment by the first roll presssection 130, and further, the embossment is flattened and a new shallowembossment is formed by the second roll press section 140.

Conversely, the height of the rugged pattern may well be set larger inthe third roller 141 located on the lower stream side, than in the firstroller 131 located on the upper stream side. In this case, thepolarizable electrode layer 18 is formed with a comparatively shallowembossment by the first roll press section 130, and further, it isformed with a deeper embossment by the second roll press section 140.

Alternatively, embossments of different shapes may well be formed insuch a way that the heights of the rugged patterns are substantiallyequalized in the first roller 131 and the third roller 141, while thepitches N₄ of the convex parts 90 b or the inclinations α thereof (referto FIG. 7) are made different from each other.

Even in the case where the embossment works for the polarizableelectrode layer 18 are performed the plurality of times in this manner,the bare portions 12 of the current collector 16 are subjected tosubstantially no embossment work when the areas 131 a ₂ and the areas141 a ₂ corresponding to the bare portions 12 of the current collector16 are made substantially smooth as shown in FIG. 17. It is thereforepermitted to relieve a damage to the current collector 16 and thewinding of the laminated product round the first roller 131.

Further, in the embodiment, only one surface of the current collector 16is formed with the polarizable electrode layer 18, but both the surfacesof the current collector 16 can also be formed with polarizableelectrode layers 18. In this case, as shown in FIG. 18, also the frontsurface 132 a of a second roller 132 included in a first roll presssection 130 may be provided with a rugged pattern. According to thismeasure, the polarizable electrode layers 18 formed on both the surfacesof the current collector 16 can be simultaneously embossed. Also in thiscase, it is permitted to relieve a damage to the current collector 16and the winding of the laminated product round the second roller 132when the rugged pattern is provided in the area 132 a ₁ havingsubstantially the same width as the width W1 of the polarizableelectrode layer 18, the other areas 132 a ₂ being made substantiallysmooth.

However, when both the first roller 131 and the second roller 132 areprovided with the rugged patterns, the polarizable electrode layers 18might fail to be sufficiently compressed in some ways of thesuperposition of the rugged patterns, or contrariwise, a damage to thecurrent collector 16 might become heavy due to excessive compression. Inorder to avoid this drawback, it is recommendable that, as shown in FIG.19, the front surface of a fourth roller 142 included in a second rollpress section 140 is provided with a rugged pattern, while the frontsurface of a second roller 132 included in a first roll press section130 is made substantially smooth. Also in this case, it is permitted torelieve a damage to the current collector 16 and the winding of thelaminated product round the fourth roller 142 when the front surface ofthe fourth roller 142 is provided with the rugged pattern in the area142 a ₁ having substantially the same width as the width W1 of eachpolarizable electrode layer 18, the other areas 142 a ₂ being madesubstantially smooth. According to this measure, the front surfaces 132a and 141 a of the other rollers 132 and 141 are substantially smooth inboth the first roll press section 130 and the second roll press section140, respectively, so that the above problem does not occur.

Besides, the manufacturing apparatus for the electrode for theelectrochemical capacitor according to the invention need not alwayshave the construction in which, as in the apparatus shown in FIG. 4, thecoating section 110, drying section 120, first roll press section 130and second roll press section 140 are arranged continuously andunitarily, but it may well be the aggregate of two or more apparatusesas long as the above order is ensured. By way of example, the sheet-likecurrent collector 16 having passed through the drying section 120 maywell be taken up once and be roll-pressed by another apparatus whichincludes the first roll press section 130 and the second roll presssection 140. Further, the first roll press section 130 and the secondroll press section 140 may well be apparatuses which are separate fromeach other. As already described, however, it is not indispensable thatthe manufacturing apparatus according to the invention includes thesecond roll press section for flattening the embossment.

Further, in the embodiment, only the polarizable electrode layer 18 issubjected to the embossment work, and substantially the whole areas ofthe bare portions 12 of the current collector 16 are not subjected tothe embossment work, but those regions of the bare portions 12 of thecurrent collector 16 which are near to the polarizable electrode layer18 may well be partially embossed as long as the above advantages of theinvention are attainable. By way of example, the width of the area 131 a₁ of the first roller 131 may well be set somewhat broad, thereby toemboss the bare portions 12 in the vicinities of the polarizableelectrode layer 18. In this case, the current collector 16 might bedamaged at the embossed parts, depending upon the height of a ruggedpattern, but the whole front surface of the polarizable electrode layer18 can be reliably embossed.

Further, in the embodiment, the embossment work (and the flattening) isperformed for the polarizable electrode layer 18 by the roll press.However, this aspect is not restrictive, but the embossment work (andthe flattening) may well be performed using a plate-shaped press devicesuch as hot press.

Besides, it suffices to perform the embossment work of the polarizableelectrode layer 18 in the region which is to be cut out as the electrodefor the electrochemical capacitor, so that the other region need not besubjected to the embossment work. By way of example, in FIG. 9, theregion except the portion cut out as the electrode 10 for theelectrochemical capacitor need not undergo the embossment work.Accordingly, substantially smooth areas may well exist at regularintervals (each being larger than the size of the electrodeto-be-cut-out) in the peripheral direction of the area 131 a ₁ of thefirst roller 131 shown in FIG. 14. Moreover, a substantially smooth areamay well exist at substantially the middle part of the first roller 131in the widthwise direction thereof, depending upon the shape of theelectrode to-be-cut-out for the electrochemical capacitor and thecoating width of the polarizable electrode layer 18. Further, the smoothareas may well be combined.

Besides, in the embodiment, the polarizable electrode layer 18 is formedby coating so that the bare portions 12 may be formed at both the endparts of the current collector 16 in the widthwise direction thereof.However, this aspect is not restrictive, but the polarizable electrodelayers 18 and the bare portions 12 may well be alternately formed atregular intervals in the lengthwise direction of the current collector16. In this case, the bare portions 12 may well be formed in such a waythat masking tape pieces are stuck on the current collector 16 at theregular intervals beforehand, whereupon the resulting structure iscoated with the polarizable electrode layer 18, which is then dried.Besides, after the embossment work has been performed with the maskingtape pieces left stuck, the masking tape pieces are stripped off. Then,the current collector 16 is bared at the corresponding parts, and thebare portions 12 having undergone no embossment work can be obtained.

Incidentally, the electrode for the electrochemical capacitor accordingto the invention can be employed as an electrode for an electricdouble-layer capacitor, and it is also utilizable as an electrode forany of various electrochemical capacitors such as a pseudo-capacitancecapacitor, a pseudo-capacitor and a Redox capacitor.

EXAMPLES

Examples of the present invention will now be described, but theinvention shall not be restricted to the examples at all.

Example 1

Granular active carbon (produced by Kuraray Chemical Co., Ltd., tradename: “RP-20”) and acetylene black (produced by Denki Kagaku KogyoKabushiki Kaisha, trade name: “Denka Black”) were mixed for 15 minutesby using a planetary mixer. The resulting mixture and fluorine rubber(produced by Du Pont Kabushiki Kaisha, trade name: “Viton-GF”) werethrown into 150 mass-parts of MIBK, and these materials were kneaded for45 minutes by using a planetary mixer. On this occasion, the compoundingproportions of the active carbon, the acetylene black and the fluorinerubber were 90.0 mass-parts, 1.0 mass-part and 9.0 mass-parts,respectively. 150 mass-parts of MIBK were further added to the kneadedmaterial obtained, and the resulting material was agitated for one hour.Thus, a coating liquid was prepared.

One surface of an aluminum foil (thickness: 20 μm) being a currentcollector was uniformly coated with the coating liquid by gravurecoating, and the MIBK was removed in a drying oven at 100° C., therebyto obtain a laminated sheet. Thereafter, the laminated sheet was passedthrough the first roll press section 130 and the second roll presssection 140 shown in FIG. 5, in the order mentioned, whereby a laminatedsheet having a thickness of 150 μm was fabricated.

Here, the height (N₃) of a rugged pattern provided in the front surface131 a of the first roller 131 was 75 μm, the pitch (N₄) of concave parts90 a was 97 μm, and the width (N₅) of each flat part 90 c was 10 μm.Besides, the inclination (α) of the concave part 90 a was set at 60°. Inaddition, press pressures based on the first roll press section 130 andthe second roll press section 140 were both set at a value of 9800 N/cm²⁽1000 kgf/cm²).

Comparative Example 1

A laminated sheet was fabricated in the same way as in Example 1, exceptthat a roll press section identical to the first roll press section 130was employed instead of the second roll press section 140.

Comparative Example 2

A laminated sheet was fabricated in the same way as in Example 1, exceptthat a roll press section identical to the second roll press section 140was employed instead of the first roll press section 130.

Comparative Example 3

A laminated sheet was fabricated in the same way as in Example 1, exceptthat the positions of the first roll press section 130 and the secondroll press section 140 were reversed.

Comparative Example 4

A laminated sheet was fabricated in the same way as in Example 1, exceptthat quite no roll press was performed. That is, a manufacturing processwas ended at the point of time at which the coating liquid on thealuminum foil being the current collector was dried.

[Evaluation]

First, how much porous grains fell off was evaluated in such a way thatthe front surface of each of the laminated sheets on the side of apolarizable electrode layer, the laminated sheets having been fabricatedby the methods of Example 1 and Comparative examples 1-4, was rubbedwith fingers.

Further, each laminated sheet was punched into a size of 20 mm×40 mm,and the punched sample was subjected to vacuum drying at temperatures of150° C.-175° C. for at least 12 hours, whereby a water content adsorbedin the porous layer was removed to fabricate an electrode for anelectrochemical capacitor. Besides, the volume capacitance of theelectrode for the electrochemical capacitor as was thus fabricated wasmeasured in the following way: First, two samples of each fabricatedelectrode for the electrochemical capacitor were prepared for an anodeand for a cathode. Subsequently, the anode and the cathode wereconfronted to each other, and a separator made of unwoven fabric ofregenerated cellulose (21 mm×41 mm, thickness: 0.05 mm, produced byNippon Kodoshi Corporation, trade name: “TF4050”) was arranged betweenthe anode and the cathode, thereby to fabricate a lamination element inwhich the anode, the separator and the cathode were stacked in touchedstates (non-junction states) in the order mentioned. Besides, ameasurement cell for the test evaluation was fabricated using thelamination element and an electrolyte solution (propylene carbonatesolution of 1.2 mol/L of triethylmethyl ammonium borofluoride).

Subsequently, the fabricated measurement cell for the test evaluationwas charged at a constant current of 2.5 mA by acharging-and-discharging test apparatus (“HJ-101SM6” produced by HokutoDenko Corporation). A situation where a voltage rose as charges wereaccumulated in the electric double-layer capacitor was monitored, theconstant-current charging was shifted to constant-voltage charging(relaxation charging) after the voltage reached 2.5 V, and theconstant-voltage charging was ended when a current became 1/10 of thecharging current. Besides, discharging was performed at the constantcurrent of 2.5 mA, and a termination voltage was made zero V. After thetest, charging was performed at a constant current of 5 mA, theconstant-current charging was shifted to constant-voltage charging aftera voltage reached 2.5 V, and the constant-voltage charging was endedwhen a current became 1/10 of the charging current. Besides, dischargingwas performed at the constant current of 5 mA, and a termination voltagewas made zero V. With such constant-current/constant-voltage chargingand discharging operations as one set, 10 sets of operations wererepeatedly performed. Total discharge energy [W·s] was found as thetemporal integral of discharge energy (discharge voltage×current (=5mA)) from a discharge curve (discharge voltage−discharge time) thusobtained, a capacitance was found in conformity with the relationformula of capacitance [F]=2×total discharge energy [W·s]/(dischargeinitiation voltage [V])², and a value obtained by dividing thecapacitance by the volume of both the electrodes (anode and cathode) wasemployed as a capacitance per unit volume (volume capacitance) [F/cm³].Incidentally, the measurement of the capacitance per unit volume wasmade under an environment of a temperature of 25° C. and a relativehumidity of 60%.

The results of the evaluation are listed in Table 1.

TABLE 1 Falling- off of First roll press Second roll Porous Volumesection press section grains capacitance Ex. 1 Presence of Absence of ∘18 F/cm³ Rugged pattern Rugged pattern Comp. ex. 1 Presence of Presenceof x 18 F/cm³ Rugged pattern Rugged pattern Comp. ex. 2 Absence ofAbsence of ∘ 16 F/cm³ Rugged pattern Rugged pattern Comp. ex. 3 Absenceof Presence of x 18 F/cm³ Rugged pattern Rugged pattern Comp. ex. 4 — —Δ 13 F/cm³ ∘ Almost no falling-off, Δ Some falling-off, and x Muchfalling-off.

As indicated in Table 1, the laminated sheet fabricated by the method ofExample 1 underwent almost no falling-off of the porous grains, and itattained a very high volume capacitance of 18 F/cm³.

In contrast, the laminated sheets fabricated by the methods ofComparative examples 1 and 3, in each of which an embossments was notflattened, attained the high volume capacitance, but they underwent muchfalling-off of the porous grains. Besides, the laminated sheetfabricated by the method of Comparative example 2, in which noembossment work was performed, underwent almost no falling-off of theporous grains, but it did not attain a sufficient volume capacitance.Further, the laminated sheet fabricated by the method of Comparativeexample 4, in which no roll press was performed, exhibited a low volumecapacitance and had the falling-off of the porous grains observed tosome extent.

It has been verified from the above that the high volume capacitance isattained with the falling-off of the porous grains prevented, byperforming the embossment work and thereafter flattening the embossment.

INDUSTRIAL APPLICABILITY

According to the present invention, it is permitted to provide amanufacturing method and a manufacturing apparatus for an electrode foran electrochemical capacitor having a high volume capacitance.

1. A manufacturing method for an electrode for an electrochemicalcapacitor, comprising: first step of forming a polarizable electrodelayer on a current collector; second step of subjecting a front surfaceof the polarizable electrode layer formed on the current collector, toan embossment work; and third step of flattening the front surface ofthe polarizable electrode layer as has undergone the embossment work. 2.A manufacturing method for an electrode for an electrochemical capacitoras defined in claim 1, wherein said first step is performed by coatingthe current collector with a coating liquid which contains porous grainshaving an electronic conductivity, a binder capable of binding up theporous grains, and a liquid capable of dissolving or dispersing thebinder therein.
 3. A manufacturing method for an electrode for anelectrochemical capacitor as defined in claim 2, wherein an electricallyconductive assistant is further contained in the coating liquid.
 4. Amanufacturing method for an electrode for an electrochemical capacitoras defined in claim 1, wherein said second step is performed by rollpress based on a roller whose front surface is provided with a ruggedpattern.
 5. A manufacturing method for an electrode for anelectrochemical capacitor as defined in claim 4, wherein a height of therugged pattern is 20% through 70% inclusive, of a thickness of thepolarizable electrode layer before performing said second step.
 6. Amanufacturing method for an electrode for an electrochemical capacitoras defined in claim 1, wherein said third step is performed by rollpress based on a roller whose front surface is substantially smooth. 7.A manufacturing method for an electrode for an electrochemical capacitoras defined in claim 1, wherein said third step is performed after saidsecond step has been performed a plurality of times.
 8. A manufacturingmethod for an electrode for an electrochemical capacitor as defined inclaim 1, wherein said third step is performed a plurality of times.
 9. Amanufacturing method for an electrode for an electrochemical capacitor,comprising: first step of coating a current collector with a polarizableelectrode layer so that a bare portion may be left at part of thecurrent collector; and second step of subjecting a front surface of thepolarizable electrode layer formed on the current collector, to anembossment work, without subjecting at least part of the bare portion ofthe current collector, to the embossment work.
 10. A manufacturingmethod for an electrode for an electrochemical capacitor as defined inclaim 9, wherein, at said first step, the current collector in a bandshape as is conveyed in a lengthwise direction thereof is coated withthe polarizable electrode layer of predetermined width so as to leavethe bare portion at, at least, one end part of the current collector ina widthwise direction thereof.
 11. A manufacturing method for anelectrode for an electrochemical capacitor as defined in claim 9,wherein said first step is performed by coating the current collectorwith a coating liquid which contains porous grains having an electronicconductivity, a binder capable of binding up the porous grains, and aliquid capable of dissolving or dispersing the binder therein.
 12. Amanufacturing method for an electrode for an electrochemical capacitoras defined in claim 11, wherein an electrically conductive assistant isfurther contained in the coating liquid.
 13. A manufacturing method foran electrode for an electrochemical capacitor as defined in claim 9,wherein said second step is performed by roll press based on a rollerwhich is partially provided with a rugged pattern.
 14. A manufacturingmethod for an electrode for an electrochemical capacitor as defined inclaim 9, wherein, at said second step, a front surface of thepolarizable electrode layer formed on the current collector is subjectedto an embossment work so as to leave part of the front surface.